Report the number of memory mappings on Linux to help diagnose limit crashes.

[marti4d]

On Linux, there is a limit of ~65536 memory mappings that can be made using mmap(). After that, future attempts may return an error code. (Here is an example crash report).

Since we already have the list of maps in the Minidump, let's print this information from Minidump-Analyzer and display it on Socorro. That way, an engineer can quickly look at the number and notice that it's rather close to the system limit, and that something might be amok.